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Why study the nitrogen contribution to the acidity of acid rain?

Hypothesis: How does the amount of nitrogen in acid rain differ in
an agricultural area as compared to an urban area?

Background: What are Nitrates and Nitrites?

Nitrates are compounds that contain one atom of nitrogen and three atoms of oxygen. Nitrites are compounds that have one atom of nitrogen and two atoms of oxygen. Nitrates are commonly in many foods, such as, some meats and especially vegetables, as well as drinking water. Nitrates are commonly used in lawn treatments and fertilizers. Nitrogen compounds are essential nutrients for plants, and nitrates are the only form when plants can take in nitrogen. Plants use nitrates from the soil which, over time, can deplete the soil of nitrates and make it difficult for future crops to grow and thrive. To help solve this problem, people treat the soil with nitrogen-based fertilizers and lawn treatments. When nitrogen-based fertilizers are used any excess nitrates can filter down into the groundwater supplies and contaminate wells. Nitrates are commonly used to indicate the overall quality of drinking water.

Why test for nitrates?

Over the last few year, people have become concerned over the nitrate levels in water supplies. This increase has been invariably linked to modern farming practices, which use nitrate based fertilizers. However, nitrates can enter the water supply from failing septic tanks and animal waste, such as manure and fertilizers. Most nitrates remain in the soil for a long period of time, and are then flushed into streams by spring rainfall. This is why during the spring months, nitrate levels tend to rise. Water supplies have always contained some level of nitrates. Natural levels of nitrates are generally less than 3 part per million. However, when these levels exceed 10 milligrams per liter, they are deemed a public hazard.

High levels of nitrates in drinking water poses a problem in young children and farm animals. What they actually do is bind to hemoglobin. Hemoglobin is the part of the red blood cell which distributes oxygen to the body's cell. Under normal conditions, the hemoglobin is an efficient transporting mechanism, easily releasing oxygen to the cells. Nitrates can only get into our blood by ingestion, mainly through water and food. Once in the blood, nitrates are converted to nitrites by a nitrate-reducing bacteria present in an infant's digestive system. The nitrites eventually which find their way into the blood and bind strongly to hemoglobin, which prevents the transfer of oxygen to the body's cells. This can cause shortness of breath, vomiting, diarrhea, heart attacks, and even death by asphyxiation. In children six months and older, the stomach acid concentrations are higher and kill the nitrogen fixing bacteria thus eliminating the possibility of nitrates being converted to nitrites.

Acid deposition of Nitrates:

Non-agricultural sources of nitrogen contribute less than 20% of the nitrogen released into the environment. Six percent is released from point sources (basically pipes) into water bodies, while 14% is deposited from atmospheric sources. The primary nitrogen source in the western United
States is agricultural fertilizers. Atmospheric deposition is the second-most prevalent source. The northeastern United States is considerably more urban and the rest of the U.S. As a consequence, atmospheric deposition is the primary source of nitrogen (accounts for one-third of the N load to watersheds).

The combustion of fossil fuels, industrial and agricultural discharges of nitrogen-containing gases, aerosols, and air-borne particles contribute to the atmospheric nitrogen load. The total atmospheric deposition of nitrogen in water bodies (directly and via rainfall) constitutes a large portion of total nitrogenous inputs to estuarine and marine systems and somewhat lessor portion of total nitrogen inputs to freshwater systems. Nitrogen is also deposited in soil and water from the atmosphere, where it enters from an array of sources, primarily as nitrogen oxide emissions from coal or oil burning electric utilities or other industries (53% of atmospheric nitrogen emissions) or from automobiles, trucks or buses (38% of atmospheric emissions). And nitrogen enters the atmosphere as it volatilizes from manure or fertilizer. Each year. 3.2 tons of atmospheric nitrogen are redo posited into watersheds in the United States, with the largest inputs in then northern and Midwestern regions.

Studies have shown that rainfall is the chief means by which biologically available nitrogen (nitrate, ammonia, some organic N) is transported to aquatic systems from the atmosphere.

Assumptions:

CO₂ levels are constant and provide a constant contribution to acid rain.
Total pH change causing acid rain is due to: CO₂, SO₂, SO₃ and NO₃, therefore, knowing the total pH, carbon dioxide amounts, SOx's and NOx's contribution can be determined using a test for either SOx's or NOx's.

Research and Testing Methods:

Determine the amount of NOx present in acid rain. Using Nitrogen, Nitrate - Cadmium Reduction Method

Introduction:
Nitrate represents the most completely oxidized state of nitrogen commonly found in water. Nitrate-forming bacteria convert nitrates into nitrates under aerobic conditions and lightning converts large amounts of atmospheric nitrogen (N2) directly to nitrates. Many granular commercial fertilizers contain nitrogen in the form of nitrates.

High levels of nitrate in water may indicate biological wastes in the final stages of stabilization or run-off from heavily fertilized fields. Nitrate-rich effluents discharged into receiving waters can degrade water quality by encouraging excessive growth of algae. Drinking waters containing excessive amounts of nitrates can cause infant methemoglobinemia (blue babies). For this reason, a maximum concentration level in drinking water has been established by the USEPA in accordance with the Safe Drinking Water Act.

The method of analysis used in the high range test in a modification of the Cadmium Reduction Method using gentisic acid in place of 1-naphthylamine. All the necessary reagents have been combined into a single stable power called NitraVer 5 Nitrate Reagent.

The low range nitrate test also is a modification of the Cadmium Reduction Method using a very sensitive chromotropic acid indicator. Both methods register nitrates and nitrite nitrogen.

Chemical Reactions: High Range
In the high range test, cadmium metal is used to reduce nitrates (NO3-) to nitrites (NO2-) (reduction 1). Next, the nitrite ions react in a acidic medium with sulfanilic acid to form an intermediate diazonium salt (reaction 2) which, when coupled with gentistic acid (reaction 3), forms an amber-colored compound. Color intensity of the compound is in direct proportion to the nitrate concentration of the water sample.

Chemical Reactions: Low Range
In the low range nitrate test, cadmium metal is used to reduce the nitrates to nitrites. The cadmium is provided in NitraVer 6 Reagent Power Pillows. Nitrite ions react with sulfanilic acid to produce an intermediate diazonium salt, as in the high range test. The diazonium salt then forms a red-orange colored complex with chromotropic acid in direct proportion to the nitrate concentration in the sample (reaction 4). In the low range test the sulfanilic acid and chromotropic acid are contained in NitriVer 3 Reagent Power Pillows.

Regional Data Collection:

Data will be collected for the amount of nitrates present in rain water in different regions. We will be collecting data throughout the up coming winter. We encourage others to participate and share their data. A format will be provided to include pertinent information.

***Rain Data Collected While at Princeton***
*Date*	*Time*	*Temperature*	*NO3 ppm*
*July 9, 1997*	*6:50 pm*	*21.5 C*	*.064 ppm*

***Rain Data Collected in Fremont***
*Date*	*Time*	*Temperature*	*NO3 ppm*

***Data Collected in Modesto***
*Date*	*Time*	*Temperature*	*NO3 ppm*

We realized that not all teachers and students would have access to a spectrophotometer so we decided to try to use a CBL unit from Texas Instruments and a light probe to see if the amount of light transmitted through a sample could be measured. We set up the light probe and a light source and in our case it was a medium sized mag light. A curvette was placed between the light source and light probe and the amount of transmission was recorded. Below is a photograph of our set up. We recorded our data in the table below and graphed the data.
CBL Light Transmission Set-Up

CBL Data Vs. Spectrophotometer

*Theoretical* *ppm*	*Dilution Ratio*	*Hach* *ppm*	*CBL No* *Filter* *Sample Only*	*CBL Green Filter with Sample*	*CBL No Sample or Filter*	*CBL with Green Filter Only*
*Sample A* *4.5 ppm*	*1:1*	*5.4 ppm*	*.961*	*.956*	*.960*	*.955*
*Sample B* *2.25 ppm*	*1:2*	*1.7 ppm*	*.959*	*.954*	*.952*	*.954*
*Sample C* *1.125 ppm*	*1:4*	*.8 ppm*	*.952*	*.950*	*.952*	*.944*
*Sample D* *.5625 ppm*	*1:8*	*.3 ppm*	*.953*	*.947*	*.946*	*.944*
*Sample E* *.28 ppm*	*1:16*	*.1 ppm*	*.954*	*.940*	*.945*	*.941*
*Sample F* *.14 ppm*	*1:32*	*.08*	*.942*	*.937*	*.937*	*.936*

Graph for Initial Data Using Standard Solutions ppm Vs. Light Transmission Using a Green Filter

Conclusion:

Additional Information:

Student Activities:

National Standards:

Inquiry based learning - Middle School
Inquiry based learning - High School